Temperature control device



July 28, 1959 M. D. MCFARLANE ETAL 2,897,331

TEMPERATURE CONTROL DEVICE Filed Nov. 9, 1955 I 3 Sheets-Sheet 1 Hal 1 N V EN TORS. MamzzoD. M FARgM'AMI film/1 Cums.

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,Filed Nov. 9, 1955 July 28, 1959 M. D. MCFARLANE ET AL 2,897,331

TEMPERATURE CONTROL DEVICE 3 Sheets-Sheet 2 AMPUFIER a PO Y Z SUE :1: 80

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TEMPERATURE CONTROL DEVICE Filed Nov. 9, 1955 3 Sheets-Sheet 3 AMPLIFIER IN VEN TORS.

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THEE ATTOENEK United States Patent C) T MPERATUR ,CQNT QL DEVICE Maynard D. McFarlane, Corona del Mar, and Cecil A.

Crafts, Pasadena, Cal vassi iw s to 'Rc er s aw-Eult n Contr l omp y, .Grs nsh 2 a co p ratio of Delaware Application November 9, 1955, Serial No. 545,860 6 a m (C Z Qr-ZD) This invention relates to heating control devices and more particularly to devices wherein the heating medium consists of a slurry of fusible material ls aying a melting temperature of a value to be controlled.

In systems requiring accurate temperature control for long periods of time wlherein temperature differentials do'not exceed a few hundredths of a degree and the system experiences varying ambient temperature conditions or heat applications, accurate control has been extremely dilficult if not impossible since present day thermostats are incapable of per-forming within such close tolerances. Such a system may comprise a crystal oscillator circuit wherein extreme frequency stability is required. Since crystal'control units are susceptible to even a slight temperature variation, drifting from the desired set frequency can be overcome only by immersing the crystal unit in an atmosphere having a continuous constant temperature condition. i

In the present invention, advantage'has been taken of the physical property exhibited by materials and alloys at their melting temperatures. The melting point of an alloy is an exactly reproducible and stable value, and may be prescribed and varied by modifying the quantity of components which go to make up the alloy. At the melting temperature, advantage is taken of the latent heat of fusion of the material used so that this exact temperature is maintained over a wide range of external temperature conditions.

At the melting temperatures, the materials consist of a slurry composed partly of solid material and partly of liquid. pendent of the ratio of liquid to solid, the slurry can be maintained at constantinternal temperature over a wide range of heat application from a heating element or thelili. In the use of an electrical heating element, extremely accurate control of the temperature oft h'e Crystal oscillator circuit; can be maintained with intermittent orWidely varying applications'of power to the heating element; Since a change ofstate' is involved at the desired temperature, which is the melting point of the alloy, the change in electrical resistance uponthis change of state has been utilized to control the amount of power delivered to the heatingelernen t. i

Forexample, with some compositions, there exists a change in resistance of approximately 90% between thesolid and liquid state of the alloy. It is, therefore, apparent that the present invention utilizes a characteristic of a fusible alloy which controls the application of heat to the system through a change occurring inthe .material itself. Thus,.the melting .temperatureof the alloy at the point of change of state or at the so-called-triple;point not only regu a e theheat applied o a heating pa but it also acts inherently as a thermostat to control the application, of heat to ,the; entire, system.

i ns s m sdiaien a the-Pres attenti th Since the melting point temperature is inde 2,897,33 l- Patented July 28 19,59

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proportional change in viscosity of the alloy in trans formingfrom'the solid state to the liquid state, is utilized to effect heating conditioiis of the alloy. Since the slurry consists of a mixture of liquid and solid material," it will be apparent, that the viscosity of the slurry is a function of the change of state, and in fact, the viscosity will vary over a very large range as the material changes-from completely solid to completely liquid. A novel arrangement of a mixing arm'andcircuit means for rotating the same is utilized to effect accurate'tem perature control of the slurry.

Therefore, it is the principal object of the present invention to utilize the melting temperature at which the change of state of .a material occurs to regulate both the heat outputof the material'and the heat producing medium applied to the material.

'Another object of the present invention is to accurately control the temperature of a'space within very precise limits for'indefinite periods of time under varying conditions ofheatapplication. I

Other objects and advantages will appear from the following specification taken in conjunction with the accompanying drawings wherein:

Pig. 1 is a schematic view of a typical arrangement of the present'invention; i i

' Fig.- 2 is a similar schematic view of another circuit menswea 'a circuit diagram of another modification of the arrangernentshownin' 2; i

'Pig. 4 is acir'cuit diagram of'stillanother modification of the present invention; and W l-Tig. '5 i is a schematic view showing ,still another arrangemento'fthe present invention. v

appear. Completelyfilling the outefj'eqmain'er 12 is 'a,

will fuse w en heated to .a'ipne c i di melting mpe tur'e, .va' id.

. Percent Sodium [60 ."iifif'if'T,""?T?" T +f For- (3., the following has been found satisfactory:

' Percent Sodium; 7-3 Gold-" 27 For 0 the following has been found satisfactory:

' Y Percent 40 n me. v, ,.I f f-1 For 93;" C .,.the following has been found satisfactory:

Percent Tin 42 Cadmium l 14 Indium '44 For 11 8: the followinghas been found satisfactory:

Ijercent Tin. 47. Indium 53 3 For 120 C., the following has been found satisfactory.

Potassium alone may be used at a temperature of 63.7 C.; sodium alone for 97.8 C. and caesium alone for 28.5 C.

A pair of electrodes 18, 20 are immersed in the material 16 and are connected to the terminals of a low .voltage-high amperage battery 22 by conductors 24, 26

through a regulating resistor 28. In order to electrically insulate the conductive material 16 from the rest of the apparatus, the containers and 12 are preferably made of insulative or non-conductive material. It will be obvious that any other suitable means may be employed to insulate the material 16, such as by coating the containers 10 and 12 with non-conductive material. It will also be apparent that the containers 10 and 12 may be made from conducting material and used as electrodes instead of the electrodes 18, 20. In addition, an agitator (not shown) may be employed for mixing the material when in a slurry state to maintain even distribution of the solid-liquid characteristics of the material 16.

In operation, since the material 16 is of a conducting nature, a current will flow from the battery 22 through the material 16, and the passage of this current will cause the liquefaction of the material 16. As heat is absorbed in the slurry state of the material 16 due to this current flow, the resistance increases, and therefore, the current is decreased. This process will reach an equilibrium when the heat generated in the material 16 exactly equals the heat lost by conduction, radiation, etc. from the container 12. The rheostat 28 serves as a means for adjusting the current flow so that this equilibrium point may be established at the temperature of liquefaction of the material 16.

Accurate temperature regulation is obtained since the material 16 is chosen to have a high latent heat of fusion so that when the material 16 is in a slurry state, any heat loss through radiation, conduction, etc., causes solidification and involves only the heat of fusion 'without effecting the temperature of the material 16. On the other hand, any gain in heat, say by an overload from the battery 22 or from any other extraneous source, will result only in absorption of this heat as the slurry mass becomes more liquid than solid. In addition, due to the inherent balancing eifect of the resistance-current values, the system is completely self-regulating once the desired characteristics have been established by adjustment of the rheostat 28.

In the modification shown in Fig. 2, the material 16 is heated by a resistance winding in the form of a heater element 30 wound around the outer container 12 and a pair of electrodes 32, 34 immersed in the material 16 which serve to sense the resistance within the material 16. The heater element 30 is connected by a conductor 36 to one terminal of a battery and to a switch arm 40 by a conductor 42. To complete the heating circuit to the heater element 30, the switch arm 40 is adapted to engage and be normally biased from a stationary contact 44 connected by a conductor 46 to the battery 38.

Actuation of the switch arm 40 into engagement with the stationary contact 44 for effecting energization of the heater element 30 is provided for and takes the form of a relay 48 having a pair of coils 50, 52, one side of each beingconnected by a wire 54. The sensing electrode 34 is connected by a conductor 56 to the other side of the coil 50. A second conductor 58 connects the sensing electrode 32 with the other side of the coil 52 through a rheostat 60 which serves to adjust the resistance within the sensing circuit at which the relay will be energized when the material 16 has reached a predetermined liquidsolid ratio in accordance with the intrinsic resistance therein. A small battery 62 of low voltage and amperage is connected in parallel with the coil 52 and the rheostat 60 and cooperates with the rheostat 60 for permitting finer adjustment and energization of the relay 48.

In operation, the current flow in the heater element 30 is turned on and off by the relay 48 in accordance with the internal resistance of the material 16 when in a predetermined stage of the slurry condition. As the liquid content in the slurry decreases, the resistance drops thus permitting an increase in the current flow therethrough whereby the relay 48 becomes energized to attract the switch arm 40 into engagement 'with the contact 44. Upon this occurrence, additional power is supplied to the heater element 30 from the battery 38 and more heat is absorbed by the material 16 to effect a greater solid to liquid ratio. When the liquid content and subsequently the resistance of the material rises, the relay 48 is deenergized and the switch arm 40 will open to cut off power to the heater element 30.

The modification shown in Fig. 3 is similar to that disclosed in Fig. 2 except that the relay 48 and its associated circuitry is replaced by a power amplifier. The sensing electrodes 32, 34 in the material 16 are connected by conductors 64, 66 respectively to one arm of a resistance bridge generally indicated by the reference numeral 68, the diagonal of which is connected by a pair of wires 70, 72 to the input stage of an amplifier 74. A pair of conductors 76, 78 connect the heater element 30 to the output stage of the amplifier 74 which derives its power from a power supply 80 through a pair of conductors 82. To complete the bridge circuit, power is supplied to the bridge 68 from the power supply 80 through a pair of wires 84, 86 in the usual manner.

The amplifier 74 may be of any conventional type wherein the input stage is adapted to sense the unbalanced voltage from the bridge 68, amplify the voltage in proportion to the electrical resistance of the material 16 as reflected by the bridge 68 and energize the heater element 30 to a degree of heat proportional to the resistance of the material 16. A rheostat 88 is connected in the wire 84 and serves to adjust the power supply to the bridge 68 thereby varying the operating level at which the amplifier 74 is required to respond.

The advantage of this embodiment over the arrangement shown in Figs. 1 and 2 is that there will be no onofi condition in the heater element 30 since the heater element will be supplied with current from the amplifier 74 at all times; however, this current will be varied in accordance with the resistance change determined by the sensing elements at the input of the amplifier 74. Under normal operating conditions, the amplifier 74 will reach a stable operating condition, and there will be very little current change experienced in the heater element 30.

The embodiment of Fig. 4 is similar to that of Fig. 3 and includes a saturable reactor in the output stage of the amplifier section of the system. As in the previous modifications, for simplicity, like components will be designated by like numerals.

Instead of directly energizing the heater element 30, the amplified signal from the amplifier 74 is fed to a saturable reactor 90 by a wire 92 to control the current to the heater element 30. As shown in Fig. 4, the conductors 76, 78 from the heater element 30 are connected to the output stage of the reactor 90 and the power supply 80 is connected to the reactor by wires 94. In this arrangement, the amplifier 74 may be of the low gain type for controlling the input winding (not shown) of the reactor 90.

While the embodiments of Figs. 1, 2, 3 and 4 are directed to the change of resistance characteristics in the slurry state of the fusible material 16, another characteristic is peculiar to the change of state of the material 16.

Since the slurry consists of a mixture, in various proportions, of the liquid and solid material, it will be apparent that viscosity of the slurry 'is a function of the change "of state, and in fact, it has been found that the viscosity w ll vary over a very large range as the material changes from entirely solid to entirely liquid. In the embodiment iof Fig. 6, a measure of viscosity is used as a sensing element for the heating control of the material 16.

In Fig. 5, a pair of mixing arms 100 are immersed n the material 16 between the containers and 12 and is connected to the operating shaft 102 of an electric motor 104 for rotation therewith. A pair of wires 106, 108 having a resistor 110 in series therewith connects the motor 104 to a source of electric current L1, L2 in the usual manner for energizing the motor 104.

The heater element 30 which is wound conductively around the outer container 12 is adapted to be energized by an amplifier 112 through a pair of conductors 114, 116 connected therebetween. The input stage of the amplifier 112 is connected across the resistor 110 by a pan of wires 118, 120, and a wire 122 connected between the source L1 and the amplifier 112 serves to complete the power supply to the amplifier 112 from the source L1, L2 through the wires 120, 122.

In operation, the voltage drop across the resistor 110 is proportional to the current drawn by the motor 104, which is in turn proportional to the mechanical resistance oifered by the slurry of the material 16 to the rotation of the steering arms 100. Thus the greater the percentage of solid material 16 in the slurry, the higher the mechanical resistance, the greater the current drawn by the motor 112, the greater the voltage drop across the series resistor 110 and consequently, the greater the signal applied to the amplifier. Since the output of the am plifier 112 is connected to the heater element 30, as the mechanical resistance is increased due to an increase in the solid content of the slurry content, the power to the heater element 30 will be increased by the amplifier 112.

It will be apparent from the foregoing that the illustrated embodiments provide new and improved control devices for maintaining steady heat to a space within precise temperature limits and which utilizes various characteristics of a slurry of fusible material to control the application of heat to the slurry so that the material is never completely solid or completely liquid. It will also be obvious to those skilled in the art that the illustrated embodiments may be variously changed and modified, or features thereof, singly or collectively without departing from the scope of the invention or sacrificing all of the advantages thereof, and accordingly the disclosure herein is illustrative only and the invention is not limited thereto.

We claim:

1. In a temperature control device, the combination comprising a container, an electrically conductive fusible material in said container having a fusion temperature coincident with a temperature to be maintained by said device and a high latent heat of fusion, a second container carried within said first mentioned container in heat transfer relationship with said fusible material and being heated thereby, a pair of electrodes connected to circuit means positioned in said fusible material for passing an electric current through said fusible material to heat same to the fusion temperature and produce a liquid-solid state thereof, the liquid content of said liquid-solid state being operable to vary the electrical resistance of said fusible material to thereby vary the heating current passing therethrough, said electrical resistance and said liquid content of said fusible material being adapted to constantly increase until the heat gained thereby and the heat lost there from reach a point of equilibrium.

2. A temperature control device as claimed in claim 1 wherein said circuit means includes a variable resistance element for adjusting the value of the current passing through said fusible material whereby said equilibrium point maybe established at the fusion temperature of said fusible material.

3. In a control device for maintaining a constant temperature condition and utilizing the latent heat ioffusion of a conductive fusible material having a fusion tempera ture coincident with the temperature to be maintained, the combination comprising a container enclosing said fusible material, a second container within said first mentioned container in heat transfer relationship with said fusible material and being heated thereby, a pair of electrodes positioned in said fusible material, circuit means including a source of potential electrically connected to said electrodes for passing a current through said fusible material to heat the same to the fusion temperature and produce a slurry thereof, and a variable resistance in said circuit means to selectively adjust the initial flow of current through said fusible material to produce said slurry, the changes in the liquid-solid content of said slurry being operative to vary the electrical resistance thereof and thereby being operative to regulate the application of heat thereto.

4. In a control device including a source of voltage, the combination comprising an electrically conductive fusible material having a high latent heat of fusion and a predetermined liquid-solid ratio in the slurry state thereof, said fusible material having an electrical resistance which increases with an increase in said liquid-solid ratio, a pair of electrodes positioned within said material, circuit means for connecting said electrodes across said source of voltage to conduct a current through said material to establish a heat input to said material, a container for said material having a predetermined heat loss to establish said ratio when the heat input to said material substantially equals the heat loss, a second container within said first mentioned container in heat transfer relationship with said fusible material, and means establishing a resistance in said circuit means to normally establish a current of predetermined magnitude for maintaining the heat input to said fusible material equal to the heat output therefrom, the value of said current being decreased by an increase in said resistance of said material in response to an increase in the liquid-solid ratio to reduce said heat input.

5. In a condition controlling device, the combination comprising a container, a conductive fusible material in said container having a fusion temperature coincident with a predetermined temperature to be maintained by said device and a high latent heat of fusion, a second container carried within said first mentioned container in heat transfer relationship with said fusible material and being heated thereby, a pair of electrodes connected to a heating control circuit and disposed in said fusible material for continuously regulating the application of heat to said fusible material in response to changes in the electrical resistance of said fusible material at the fusion temperature thereof to maintain the heat input thereto coincident with the heat loss therefrom.

6. A temperature stabilizing and control apparatus comprising a first container, a second container carried Within said first container, an electrically conductive fusible material having a fusion temperature coincident with a predetermined temperature to be maintained by said apparatus and a high latent heat of fusion carried within said first container in heat transfer relationship with said second container for heating same, a pair of electrodes connected to circuit means and positioned in said fusible material for passing an electrical current through said fusible material to heat same to the fusion temperature and produce a slurry thereof, said circuit means being operable to continuously regulate the current passing through said fusible material in response to change in resistance of said fusible material to maintain a heat input thereto equal to the heat loss therefrom.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Chubb et a1. Feb. 1, 1921 Hands Mar. 3, 1925 Kubo July 5, 1927 Hentschel Apr. 18, 1933 Stallard Aug. 8, 1933 8 MacFarlane May 16, 1939 Hartwig et a1. July 25, 1950 Colander et a1. Oct. 10, 1950 Gilbert May 26, 1953 Dunlap Dec. 6, 1955 Throw Sept. 11, 1956 Welch Oct. 16, 1956 

